MergeIntervals.cs

public class Program
{
    public static void Main(string[] args)
    {
        var input = new List<(int, int)>()
        {
            (1, 3),
            (8, 10),
            (2, 6),
            (15, 18)
        };
        var output = MergeIntervalsLinq(input);
    }

    public static List<(int Start, int End)> MergeIntervalsLinq(List<(int Start, int End)> intervals)
    {
        if (intervals.Count == 0)
            return [];

        return intervals
            .OrderBy(i => i.Start) // Sort by start time
            .Aggregate(
                new List<(int Start, int End)>(), // Seed: empty result list
                (merged, current) =>
                {
                    if (merged.Count == 0 || merged[^1].End < current.Start)
                    {
                        // No overlap — add new interval
                        merged.Add(current);
                    }
                    else
                    {
                        // Overlap — extend the last interval
                        var last = merged[^1];
                        merged[^1] = (last.Start, Math.Max(last.End, current.End));
                    }

                    return merged;
                });
    }
}